Filter system for viscous or highly viscous liquids, in particular plastic melts and method for filtering viscous or highly viscous liquids

ABSTRACT

A device and a method for filtering viscous or highly viscous liquids, in particular plastics melts, includes use of an oscillating filter plate.

BACKGROUND OF THE INVENTION

The invention relates to a method and an apparatus for filtering viscousor highly viscous liquids, in particular plastics melts, using a filterplate.

To remove contaminants from viscous or highly viscous liquids, inparticular plastics melts, the prior art generally uses filtrationapparatuses which use various filter embodiments.

Contaminants which frequently occur in viscous or highly viscousliquids, such as for example plastics melts, are for example organic orinorganic contaminants, such as metals, mineral substances and the like,or contaminants resulting from other polymers, foreign particles,excessively coarse added substances and additives and agglomeratesthereof. Further problematic contaminants are for example degradationproducts of the viscous or highly viscous liquid, which arise in use,production or other proper or improper uses, for example exposure toexcessive temperatures, or during production, for example in the case ofplastics, by excessive or inadequate crosslinking, such as for examplegels.

The filters used in this respect are in particular sieve plates orindeed filter belts or “belt filters”.

In any event, the openings in the corresponding filter must be smallerthan the contaminants to be retained and separated from the viscous orhighly viscous liquid.

As a result of deposition of the contaminants on the filter belt orsieve plate, the degree of contamination of the respective filter unitused increases more or less quickly as a function of the degree ofcontamination of the viscous or highly viscous liquid and the throughputthereof through the filtration apparatus. In the worst case, this mayresult in as good as no liquid any longer being able to pass through thefilter.

As a function of the filter embodiment used, a sieve plate musttherefore for example be replaced or back-flushed. Cleaning thenproceeds as a function of the degree of contamination or pressurebuild-up or at fixed times.

This generally means that material flow is not continuous, since themelt may be passed through other chambers during replacement or theback-flushing process, possibly resulting in pressure pulses and thelike. Filtration conditions undergo change as a result of the pressurebuild-up which occurs until the filter is exchanged. Precisely in thecase of highly contaminated materials with extensive, sheet-likecontaminants, the filter may very rapidly become blocked, so resultingin very frequent exchange cycles interrupting material flow.

For this reason, a filtration system with continuous cleaning of thefilter is highly advantageous.

In continuous systems, the filter is cleaned, for example, by rotating aplate provided with fine holes or a cylinder, or cleaning is performedconstantly by a rotating scraper or a screw mounted in the materialstream on the sieve surface. In the process, the contaminants areconveyed outwards through suitable transport ducts and pressure-reducingmechanisms.

A disadvantage here is the mechanical contact between the cleaningapparatus and the sieve plate or the filter belt, which, in particularin the case of high levels of mineral or metallic contamination, leadsto high levels of wear to the sieve plate or the filter belt. Moreover,in most systems relatively large dead volumes arise, with long materialholding times, which may lead to melt degradation.

When cleaning the filter plate, for example, using scrapers, screws andthe like, melt does not flow through the cleaning zone and a “food milleffect” arises, i.e. comminution of the contaminants and thus passage ofthe contaminants through the filter plate.

A filter apparatus is known, for example, from AT 404562 B for liquidscontaining contaminants, in which the filter is cleaned by a scraperelement.

A filter apparatus is known from DE 10 2016 202 489 which comprises aninlet chamber, an outlet chamber and a filter system separating inletchamber and outlet chamber, wherein the inflow direction of the liquidto be filtered is at an angle of between 10° and 90°, in particularbetween 30° and 70°, relative to the surface normal of the filter. Thistangential inflow to the filter enables very small chamber volumes.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a filter apparatus forfiltering viscous or highly viscous liquids, in particular plasticsmelts, which allows continuous operation and additionally the avoidanceof the disadvantages of the prior art, in particular wear to the filterplate.

The present invention accordingly provides a filter system comprising afilter plate situated in a filter chamber, which is supported by afilter support plate, characterized in that either the filter plate isguided on the filter support plate by sliding elements in grooves or thefilter support plate with the filter plate situated thereon is guided inthe filter chamber by sliding elements and the filter plate or thefilter plate together with the filter support plate is guided in anoscillating motion to clean the filter plate.

The present invention also provides a method for filtering viscous orhighly viscous liquids, in particular plastics melts, including thefollowing method steps

-   -   supplying the viscous or highly viscous liquid to a filter        chamber, in which a filter plate is situated which is guided in        the filter chamber at the bottom and/or sides by sliding        elements and which is guided in an oscillating motion    -   supplying the viscous or highly viscous liquid to the filter        chamber through an inlet opening    -   carrying away the liquid passing through the filter plate    -   moving the filter plate to a cleaning chamber    -   carrying away the contaminants present on the filter plate by        way of the cleaning chamber using conveying devices or a        back-flushing process.

In this case, during the filter cleaning process no cleaning apparatuspasses over the surface or relative to the surface of the filter plate,but rather the filter plate is moved by the motion on one side orsymmetrically on each side to a cleaning chamber. A cleaning apparatus,for example a scraper, does not pass over the surface of the filterplate or relative thereto, but rather the filter plate is moved by themotion into one side or symmetrically on each side of the cleaningchamber. In this way, the cleaning process is uncoupled from thefiltration process.

One substantial advantage is that during cleaning of the filter platemelt continues to flow through the latter in the filter zone and theoccurrence of the “food mill effect”, i.e. comminution of thecontaminants and thus passage of the contaminants through the filterplate is thus virtually eliminated. In particular, gels present in themelt may be removed extremely effectively and are not forced through thefilter plate during cleaning. The filter zone is that region in whichthe liquid to be filtered passes through the filter plate and the filtersupport plate.

No filtration takes place in the cleaning zone.

Since there is also no scraper resting constantly on the plate, wearfrom hard contaminants of the melt, such as mineral or metalliccontaminants, may also be greatly reduced.

According to the invention, the filter plate may be embodied as a solidsieve plate or indeed consist of a stack of one or more filter mats orsheets.

The sieve plate may in this case take the form of a solid plate withholes, which are produced for example by drilling, electric dischargemachining, water jet, lasers, electron beam, particle beams (for exampleprotons), by etching or the like.

In this case, depending on the embodiment, the filter plate ispreferably at least twice as wide as the active filter area in thefilter zone.

The filter plate or the filter support plate is guided at the bottom andsides for example via sliding elements in grooves, wherein the slidingelements may consist of low-wear materials or bearing materials, such asfor example copper, aluminium bronzes, sintered elements or the like.The melt itself may here also form a thin lubricant film.

The filter plate may be supported in the filter chamber by a filtersupport plate, which likewise comprises openings for passage of themelt.

The filter support plate is in any event embodied in such a way that itensures an optimum compromise between permeability, i.e. low flowresistance, and optimum strength. The openings in the filter supportplate may be round, polygonal, in the form of elongate holes and thelike and arranged perpendicular or at an angle to the surface in orderfor example to allow better flow distribution. The cross-section anddirections may also vary in the longitudinal profile of the openings.

The filter support plate may moreover take the form of a plurality oflayers, materials and combinations.

Thus, for example, the surface may be embodied with a particularlyfriction-reducing soft or hard layer or texture in order for example tofacilitate sliding of the filter element.

A particularly firm, tension-resistant material may be arranged underthe surface of the filter support plate. The filter support plate hereconsists for example of hardened steel, on the surface of which isapplied a material with good sliding properties, such as for instancebronze.

In one embodiment, the filter plate may be moved to and fro, i.e.oscillated, in the filter chamber over the stationary filter supportplate during the filtration process. The stationary filter support platethen acts as a separator in the melt stream.

In this case, the filter plate preferably takes the form of a solidplate, since it must be able directly to absorb the forces which ariseas a result of the plate being pushed to and fro.

In a further embodiment of the invention, the entire filter plate withthe filter support plate arranged therebelow may oscillate, said filtersupport plate at the same time absorbing the force arising from thepressure difference in the melt stream.

In this case, the filter plate may take the form of a thin plate, sheetor mat, since it does not have to absorb any thrust forces. The forcewhich is needed to move the filter plate and the filter support platenecessary is in this case greater than in a case where only the filterplate is moved.

A combination of these embodiments is, however, also possible, whereinfor example a compact but thin filter plate is oscillated over a filtersupport plate. Suitable measures must then be taken to absorb the higherfriction forces which arise as a result of the high melt pressure. Thisis achieved in particular by the sliding elements being of low-wearmaterials or bearing materials.

Motion or oscillation of the filter plate or of the filter plate and thefilter support plate may be brought about by an electrical, hydraulic,pneumatic or other mechanical drive.

A cleaning chamber is arranged on one or both sides of the filterchamber.

This cleaning chamber is arranged somewhat higher in the filter inflowdirection than the filter plate itself, in order additionally to take upcontaminants at the surface. The cleaning chamber is embodied byblocking elements which, alone or in combination additional cleaningelements, seal the cleaning chamber relative to the filter chamber.

The blocking and/or cleaning elements may be moved mechanically, underthe control of levers or links, by a reciprocating motion, by springs,by melt pressure, or independently electrically, mechano-pneumaticallyor hydraulically. The contact pressure of the blocking and/or cleaningelements may be varied as desired, depending on application.

Scraper units may preferably be considered as cleaning elements. Thescrapers themselves are mounted replaceably on a base unit. The scrapersmay in this case consist of metals or alloys. Sandwich structures mayhowever also be provided, which are in each case also provided withdifferent surface coatings such as PVD or CVD, DLC or ceramic layers, orof plastics and combinations thereof. What is essential here is thecombination of the materials of scraper and sieve, in order on the onehand to enable optimum cleaning and on the other hand to keep wearlevels low.

The scrapers are in this case embodied as wedges, blades, cutters,rollers, slats, a driven screw or as a combination of such embodiments.In one particular embodiment, a cleaning apparatus may also beincorporated; in this way, one or more scrapers are for example guidedthrough a slotted plate during the backwards movement and thecontaminants are scraped off as they are drawn through.

Depending on contaminant, materials, filter material etc., with thissystem the contact pressure may be varied virtually at will so as toenable an optimum cleaning action with minimum filter wear.

The filter plate is moved by at least one slider, which seals thecleaning chamber from the outside.

In one particular embodiment, the filter plate may ultimately beembodied such that sealing is achieved by raising the filter plate tothe height of the cleaning chamber itself.

Furthermore, a plurality of sealing and/or cleaning elements may also bearranged in series.

The plate is then moved into the cleaning chamber, the piston beingmoved to the side to open up the volume of the cleaning chamber. In thisphase, the actual cleaning elements are not or only slightly in contactwith the plate surface. Only once part, for example half, of the platehas been introduced into a cleaning chamber is the latter substantiallysealed from the filter chamber by the blocking and/or cleaning elements.

Then an outflow duct, which may comprise corresponding elements such asactive or passive screws, helices or labyrinth-type structures, isopened by means of a valve or by the geometry of the filter plate.Moreover, the outflow duct may be separated thermally from the filterand in this way the viscosity of the outflowing material may bepurposefully influenced by dedicated heating or cooling systems.

The valves may be embodied as pistons, ball valves, slide valves, orlinear or rotating, and may be mechanically, pneumatically orhydraulically actuatable.

In one specific embodiment, the blocking and cleaning sliders may takethe form of valves.

A profile channel may here be mounted along the slider, for example, viawhich the contaminants are passed to a duct incorporated into theslider. In the cleaning cycle, this slide valve is in contact with thefilter. In precisely this position the duct incorporated into the sliderlies in the same plane as a bore in the slider support plate and thusopens up a duct to the outside directly or by way of above-statedpressure-reducing elements, via which duct the contaminants are passedto the outside.

In this embodiment, it is possible to dispense with further valve units.

The filter plate is then moved in the opposite direction. The slider orthe end of the filter plate then reduces the volume of the cleaningchamber and at the same time the surface of the filter plate is cleanedby the blocking wedges or additional scraper profiles, rotating screws,rollers and the like. The contaminants are discharged into the cleaningchamber together with the remainder of the melt.

To simplify discharge over the width, the sliders or cleaning elementsare arranged for example obliquely or also in the shape of a V. In thecase of the V-shaped arrangement of the cleaning elements, two ducts areprovided.

In a further embodiment, two cleaning chambers may be provided.

In this case, the filter is cleaned on one side only to a good half orpreferably a good ⅓ of the total length of the filter in the firstchamber and at the same time is introduced on the opposite side into thesecond symmetrically arranged chamber.

As a result of the specific construction, it is also possible toback-flush the filter area with a stream of material from the oppositeside when cleaning, i.e. before or during pushing back into the activeposition.

For this purpose, material is forced actively by an actively drivenvalve or by corresponding overflow ducts from the clean side towards thenow almost pressureless opposite side in the cleaning chamber.

As an alternative, however, a volume of material with filtered materialmay also be provided on the bottom of the cleaning chamber in such a wayas to enable a stream of cleaned material at the bottom during movementof the filter into the cleaning chamber. To this end, overflow ducts areprovided which are open in the end position of the support or filterplate. During the cleaning motion, these overflow ducts are closed andthe clean material is forced from underneath through the filter supportplate and the filter plate.

Since on insertion of the filter plate into the cleaning chamber, meltmay also be filtered into the filter chamber and through the filterplate, such backflushing may also take place to a lesser degree withoutthe use of overflow ducts.

Naturally, specific backflow valves may also be inserted in thedischarge ducts. It is also possible, after the cleaning process, tomodify the properties of the melt, for example, by applying activesubstances, additives, catalysts etc. via suitable metering valves andapparatuses or via the scraper elements, past which the filter platemoves in the opposite direction in order to bring it back into thefiltration position.

According to a further embodiment, two filter chambers are eachconnected to a common melt duct by means of a switchable valve, in sucha way that, when the valve is in the one state, the melt runs throughthe first filter chamber and, when the switchable valve is in the otherstate, the melt runs through the second filter chamber.

The valve is configured such that parallel operation is possible. Threeor more filter chambers may also be connected in parallel by way of suchvalves, such that at least one of the filters always ensures melt flow.

In a further embodiment, two or more filter chambers may be arranged oneabove the other or next to one another in series, such that the outflowof the preceding one is connected to the inflow of the subsequent oneand the melt passes successively through the two or more belt filters.

Discharge of the contaminants in the form of the filter cake may proceedsideways in the direction of the sieve motion or at 90° thereto orupwards. What is important here is that in the process the contaminantsundergo a pressure reduction to atmospheric pressure.

In the simplest case, this is achieved by a helix or conveying screw. Tobe able actively to convey the contaminants outwards downstream of thechamber valve, a dedicated helix or conveying screw may convey thematerial outwards on each side or, if the discharge ducts converge, thismay proceed with a common helix or conveying screw. No further excessivedegradation of the melt must take place in the process, so as not togenerate deposits in the discharge region.

In a further embodiment, the material may however be actively cooledduring discharge, such that only high-viscosity or even solidifiedcontaminants arrive outside. To this end, a cold duct decoupledthermally from the heated system is provided in the filter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 9 show embodiments according to the invention. In particular:

FIGS. 1a-1c show a method for cleaning the filter;

FIGS. 2a-2c show a method for cleaning the filter with freeback-flushing;

FIGS. 3a-3c show a filtration method with forced back-flushing;

FIG. 4 shows an embodiment of the filter;

FIG. 5 shows an embodiment of the filter in which only the filter plateis oscillated;

FIG. 6 shows an embodiment for conveying away the filter cake;

FIG. 7 shows an embodiment in which the filter cake is conveyed away ina controlled manner by a conveying screw;

FIG. 8 shows cooling ducts in the cleaning chamber for conveying awaythe filter cake; and

FIG. 9 shows an embodiment according to FIG. 7, in which the pressure isreduced by active cooling by cooling ducts.

DETAILED DESCRIPTION OF THE INVENTION

In the description below, the following reference numbers are used:

-   1 the filter chamber-   2 the filter plate-   3 the filter support plate-   4 the contaminants (filter cake)-   5, 5 a a cleaning chamber-   6, 6 a a blocking slider with integral valve-   7 the discharge duct in the cleaning chamber-   8 plain bearings-   9 a conveying screw for conveying away the filter cake-   10 the viscous or highly viscous liquid to be filtered, for example    the plastics melt to be filtered-   11 the filtrate of the viscous or highly viscous liquid-   12 a blocking element-   13 an insulating layer-   14 heating or cooling ducts-   15 the melt chamber for back-flushing-   15 a the back-flushed melt-   16 the slider for moving the filter or the filter support plate-   17 the melt inlet-   18 the melt outlet-   19 a shut-off element for forced back-flushing-   20 solidified contaminant material-   21 the cleaning zone-   22 the filter zone.

FIGS. 1a-1c show a method for cleaning the filter in which the filter iscleaned without back-flushing.

The device consists in this respect of a filter chamber 1 and a filterplate 2, which is supported by a filter support plate 3.

As shown in FIG. 1a , the contaminants settle on the filter plate 2 asfilter cake 4 during the course of the process of filtering a viscous orhighly viscous liquid 10.

To clean the filter plate 2 of the filter cake 4, the valve 6, which inthis case takes the form of a piston, is actuated and the filter cake 4is passed into the cleaning chamber 5 and removed from the cleaningchamber through the duct 7. Removal of the filter cake 4 proceeds bydisplacing the filter plate 2 optionally together with the filtersupport plate 3 in the direction of the arrows, wherein the filter plate2 is transported to a second cleaning chamber 5 a and the process forcomplete cleaning of the filter plate is carried out.

FIGS. 2a-2c show a method for cleaning the filter with freeback-flushing.

Here, the pressure difference up- and downstream of the filter plate 2which arises during cleaning of the filter ensures that some of thefiltrate 11 from the melt chamber is forced back for back-flushing 15through the filter support plate 3 and the filter plate 2 in theback-flushing zone 21 below the filter cake 4 (FIG. 2b ). The filtercake 4 is lifted up by the back-flushed melt 15 a and in this way forcedmore readily into the duct 7 of the cleaning chamber 5.

Removal of the filter cake 4 proceeds by displacing the filter plate 2optionally together with the filter support plate 3 in the direction ofthe arrows, wherein the filter plate 2 is transported to a secondcleaning chamber 5 a and the process for further cleaning of the filterplate is carried out.

FIGS. 3a-3c show a filtration method with forced back-flushing. Here theback-flushing process is initiated by sealing the back-flushing zone 15by the slider motion. The filter system here comprises an additionalshut-off element 19. The material is forced through the filter frombelow with elevated pressure and the filter plate cleaning process iscarried out as in the procedure shown in FIG. 2.

FIG. 4 shows an embodiment of the filter, in which filter plate 2 andfilter support plate 3 oscillate together, i.e. are pushed to and fro.The filter support plate 3 is here mounted in the filter chamber 1 onplain bearings 8.

FIG. 5 shows an embodiment of the filter in which only the filter plate2 is oscillated. In this case, the filter plate 2 is mounted on plainbearings 8 which are situated on the filter support plate 3.

FIG. 6 shows an embodiment for conveying away the filter cake 4 out ofthe cleaning chamber. In this case, in duct 7 modification of thecross-section reduces the pressure from a pressure level P1 to apressure level P0, the filter cake 4 thereby being conveyed out of theduct

In FIG. 7, filter cake 4 is conveyed away in a controlled manner bymeans of a conveying screw 9.

In FIG. 8, cooling ducts 14 are provided in the cleaning chamber forconveying away the filter cake 4, such that the pressure in the cleaningchamber is reduced by cooling. The insulating layer 13 serves todecouple the temperature of the discharge duct 7, and thus thetemperature of the material to be discharged may be reduced and theviscosity increased by a lower temperature than in the filter.

FIG. 9 shows an embodiment according to FIG. 7, in which the pressure ishowever reduced by active cooling by cooling ducts 14. Solidifiedmaterial thereby exits from the end of the discharge duct 2.

1. A filter system comprising: a filter chamber which defines an activefilter area in a filter zone; at least one cleaning chamber connected tothe filter chamber; a filter plate arranged in the filter chamber, thefilter plate being at least twice as wide as the active filter area; anda filter support plate arranged in the filter chamber, the filter platebeing supported by the filter support plate, wherein the filter plate ismovable to the at least one cleaning chamber to clean the filter plate,wherein either (i) the filter plate is guided on the filter supportplate, by sliding elements in grooves, in an oscillating motion relativeto the filter support plate to clean the filter plate, or (ii) thefilter support plate is guided in the filter chamber by sliding elementssuch that the filter plate together with the filter support plate isguided in an oscillating motion to clean the filter plate.
 2. (canceled)3. The filter system according to claim 1, wherein the at least onecleaning chamber is sealed relative to the filter chamber by one or moreblocking elements.
 4. The filter system according to claim 1, furthercomprising a cleaning apparatus in the form of a scraper unit.
 5. Thefilter system according to claim 1, wherein the filter plate takes theform of a plate, sheet or mat.
 6. The filter system according to claim1, wherein a conveying screw is provided in the at least one cleaningchamber for discharging a filter cake.
 7. A method for filtering viscousor highly viscous liquids, comprising: supplying the viscous or highlyviscous liquid to a filter chamber which defines an active filter areain a filter zone, the filter chamber having a filter plate supported bya filter support plate, the filter plate being at least twice as wide asthe active filter area, wherein either (i) the filter plate is guided onthe filter support plate, by sliding elements in grooves, in anoscillating motion relative to the filter support plate, or (ii) thefilter support plate is guided in the filter chamber at the bottomand/or sides by sliding elements such that the filter plate togetherwith the filter support plate is guided in an oscillating motion;supplying the viscous or highly viscous liquid to the filter chamberthrough an inlet opening; carrying away the liquid passing through thefilter plate; moving the filter plate to a cleaning chamber; andcarrying away contaminants present on the filter plate by way of thecleaning chamber.
 8. The method according to claim 7, wherein thecarrying away of the contaminants present on the filter plate isperformed by a back-flushing process initiated by a pressure differenceup- and downstream of the filter plate.
 9. The method according to claim7, wherein the carrying away of the contaminants present on the filterplate is performed by a back-flushing process initiated by sealing aback-flushing zone.
 10. The method according to claim 7, wherein thecarrying away of the contaminants present on the filter plate isperformed by using conveying devices.
 11. The method according to claim7, wherein during cleaning of the filter plate, the viscous or highlyviscous liquid continues to flow through the filter plate in the filterzone.
 12. The filter system according to claim 3, wherein the one ormore blocking elements may be moved mechanically, under the control oflevers or links, by a reciprocating motion, by springs, by meltpressure, or independently electrically, mechano-pneumatically orhydraulically.
 13. The filter system according to claim 3, wherein theone or more blocking elements are formed with an integral valve, bywhich a filter cake is removable from the cleaning chamber.
 14. Thefilter system according to claim 1, further comprising first and secondcleaning chambers arranged on opposite sides of the filter zone,respectively.
 15. The filter system according to claim 1, furthercomprising first and second blocking sliders arranged on opposite sidesof the filter zone, respectively.
 16. The filter system according toclaim 1, further comprising first and second slider elements arranged onopposite sides of the filter support plate, respectively.
 17. The filtersystem according to claim 14, wherein the filter plate and the filtersupport plate are arranged such that, due to either the oscillatingmotion of the filter plate relative to the filter support plate or theoscillating motion of the filter plate together with the filter supportplate, one portion of the filter plate can be filtering by flowingunfiltered liquid from an unfiltered chamber through the active filterarea to a filtered chamber, while another portion of the filter plate isbeing cleaned in one of the first and second cleaning chambers.
 18. Thefiltration system according to claim 1, wherein the filter plate isselected from the group consisting of a belt, a sheet, a plate or a mat.19. The filtration system according to claim 15, wherein each of theblocking sliders includes an integral valve.
 20. The filtration systemaccording to claim 19, further comprising first and second cleaningchambers arranged on opposite sides of the filter zone, respectively,each cleaning chamber having a discharge duct, wherein each of theblocking sliders defines a fluid passage capable of permitting anyback-flushed liquid to flow to the discharge duct of one of the cleaningchambers.